Method for forming integrated circuit devices using a phase shifting mask

Abstract

Integrated circuits with small feature sizes are obtained using a phase shifting mask which has reduced back reflection and improved optical contrast. These improvements result from reduced etching of the chrome and chrome oxide layers on the phase shifting mask. In one embodiment, the phase shifting mask is formed by depositing an image reversible photoresist layer (22) which overlies the optical mask (18). Forming a first exposed region (24) and an unexposed region (26) in the image reversible photoresist layer (22). Treating the first exposed region (24) to form a hardened first exposed region. Forming a second exposed region (30) within the remaining portion of the unexposed region (26) by exposing the back surface (16) of the substrate (12) to an optical illumination source. Removing the second exposed region (30) to uncover a portion (32) of the substrate (12) and to form an etch mask (34). The uncovered portion (32) of the substrate (12) is etched to form a trench region (38).

We claim: 
     
       1. A device fabrication method comprising the steps of: providing a substrate wherein the substrate is transparent to ultraviolet radiation with a wavelength greater than 190 nanometers, the substrate having a front surface and a back surface;   forming an optical mask overlying the front surface of the substrate, the optical mask being opaque to ultraviolet radiation with a wavelength greater than 190 nanometers;   depositing an image reversible photoresist layer overlying the optical mask;   forming a first exposed region and an unexposed region in the image reversible photoresist layer, the first exposed region having a sidewall wherein the sidewall overlies a portion of the optical mask;   treting the first exposed region to form a hardened first exposed region;   exposing the back surface of the substrate to an optical illumination source, wherein radiation from the optical illumination source passes through a portion of the substrate to form a second exposed region that lies within a remaining portion of the unexposed region;   removing the second exposed region to uncover a portion of the substrate and to form an etch mask, the etch mask comprising the hardened first exposed region and the remaining portion of the unexposed region;   etching the uncovered portion of the substrate to form a trench region; and   removing the etch mask to form a phase shifting mask.   
     
     
       2. The method of claim 1, wherein the step of forming the optical mask is further characterized as forming the optical mask of chrome with an overlying layer of chrome oxide. 
     
     
       3. The method of claim 1, wherein the step of treating the first exposed region comprises the step of: heating the first exposed region to form a hardened first exposed region.   
     
     
       4. The method of claim 1, wherein the step of treating the first exposed region comprises the steps of: heating the first exposed region; and   exposing the first exposed region to an amine vapor to form a hardened first exposed region.   
     
     
       5. A device fabrication method comprising the steps of: providing a substrate wherein the substrate is transparent to ultraviolet radiation with a wavelength greater than 190 nanometers, the substrate having a front surface and a back surface;   forming a phase shifting layer of material overlying the front surface of the substrate, the phase shifting layer being transparent to ultraviolet radiation with a wavelength greater than 190 nanometers;   forming an optical mask overlying the the phase shifting layer, the optical mask being opaque to ultraviolet radiation with a wavelength greater than 190 nanometers;   depositing an image reversible photoresist layer overlying the optical mask;   forming a first exposed region and an unexposed region in the image reversible photoresist layer, the first exposed region having a sidewall wherein the sidewall overlies a portion of the optical mask;   treating the first exposed region to form a hardened first exposed region;   exposing the back surface of the substrate to an optical illumination source, wherein radiation from the optical illumination source passes through a portion of the substrate to form a second exposed region that lies within a remaining portion of the unexposed region;   removing the second exposed region to uncover a portion of the phase shifting layer and to form an etch mask, the etch mask comprising the hardened first exposed region and the remaining portion of the unexposed region;   etching the uncovered portion of the phase shifting layer to form a trench region; and   removing the etch mask to form a phase shifting mask.   
     
     
       6. The method of claim 5, wherein the step of forming the optical mask is further characterized as forming the optical mask of chrome with an overlying layer of chrome oxide. 
     
     
       7. The method of claim 5, wherein the step of treating the first exposed region comprises the step of: heating the first exposed region to form a hardened first exposed region.   
     
     
       8. The method of claim 5, wherein the step of treating the first exposed region comprises the steps of: heating the first exposed region; and   exposing the first exposed region to an amine vapor to form a hardened first exposed region.   
     
     
       9. A method of fabricating an integrated circuit comprising the steps of: providing a substrate wherein the substrate is transparent to ultraviolet radiation with a wavelength greater than 190 nanometers, the substrate having a front surface and a back surface;   forming a phase shifting layer of material overlying the front surface of the substrate, the phase shifting layer being transparent to ultraviolet radiation with a wavelength greater than 190 nanometers;   forming an optical mask overlying the phase shifting layer, the optical mask being opaque to ultraviolet radiation with a wavelength greater than 190 nanometers;   depositing an image reversible photoresist layer overlying the optical mask;   forming a first exposed region and an unexposed region in the image reversible photoresist layer, the first exposed region having a sidewall wherein the sidewall overlies a portion of the optical mask;   treating the first exposed region to form a hardened first exposed region;   exposing the back surface of the substrate to an optical illumination source, wherein radiation from the optical illumination source passes through a portion of the substrate to form a second exposed region that lies within a remaining portion of the unexposed region;   removing the second exposed region to uncover a portion of the phase shifting layer and to form an etch mask, the etch mask comprising the hardened first exposed region and the remaining portion of the unexposed region;   etching the uncovered portion of the phase shifting layer to form a trench region; and   removing the etch mask to form a phase shifting mask;   providing a semiconductor substrate;   coating the semiconductor substrate with a photoresist layer to form a photoresist coated semiconductor substrate;   placing the phase shifting mask adjacent to the photoresist coated semiconductor substrate;   transmitting light through a portion of the phase shifting mask to define an exposure pattern in the photoresist layer; and   developing the photoresist layer to form a photoresist mask overlying the semiconductor substrate.   
     
     
       10. A method of fabricating an integrated circuit comprising the steps of: providing a substrate wherein the substrate is transparent to ultraviolet radiation with a wavelength greater than 190 nanometers, the substrate having a front surface and a back surface;   forming an optical mask overlying the front surface of the substrate, the optical mask being opaque to ultraviolet radiation with a wavelength greater than 190 nanometers;   depositing an image reversible photoresist layer overlying the optical mask;   forming a first exposed region and an unexposed region in the image reversible photoresist layer, the first exposed region having a sidewall wherein the sidewall overlies a portion of the optical mask;   treating the first exposed region to form a hardened first exposed   exposing the back surface of the substrate to an optical illumination source, wherein radiation from the optical illumination source passes through a portion of the substrate to form a second exposed region that lies within a remaining portion of the unexposed region;   removing the second exposed region to uncover a portion of the substrate and to form an etch mask, the etch mask comprising the hardened first exposed region and the remaining portion of the unexposed region;   etching the uncovered portion of the substrate to form a trench region; and   removing the etch mask to form a phase shifting mask;   providing a semiconductor substrate;   coating the semiconductor substrate with a photoresist layer to form a photoresist coated semiconductor substrate;   placing the phase shifting mask adjacent to the photoresist coated semiconductor substrate;   transmitting light through a portion of the phase shifting mask to define an exposure pattern in the photoresist layer; and   developing the photoresist layer to form a photoresist mask overlying the semiconductor substrate.   
     
     
       11. A device fabrication method comprising the steps of: providing a substrate wherein the substrate is transparent to ultraviolet radiation with a wavelength greater than 190 nanometers, the substrate having a front surface and a back surface;   forming an optical mask overlying the front surface of the substrate, the optical mask being opaque to ultraviolet radiation with a wavelength greater than 190 nanometers;   forming a phase shifting layer of material overlying the optical mask, the phase shifting layer being transparent to ultraviolet radiation with a wavelength greater than 190 nanometers;   depositing an image reversible photoresist layer overlying the phase shifting layer;   forming a first exposed region and an unexposed region in the image reversible photoresist layer, the first exposed region having a sidewall wherein the sidewall overlies a portion of the optical mask;   treating the first exposed region to form a hardened first exposed region;   exposing the back surface of the substrate to an optical illumination source, wherein radiation from the optical illumination source passes through a portion of the substrate to form a second exposed region that lies within a remaining portion of the unexposed region;   removing the second exposed region to uncover a portion of the phase shifting layer and to form an etch mask, the etch mask comprising the hardened first exposed region and the remaining portion of the unexposed region;   etching the uncovered portion of the phase shifting layer to form a trench region; and   removing the etch mask to form a phase shifting mask.   
     
     
       12. The method of claim 11, wherein the step of forming the optical mask is further characterized as forming the optical mask of chrome with an overlying layer of chrome oxide. 
     
     
       13. The method of claim 11, wherein the step of treating the first exposed region comprises the step of: heating the first exposed region to form a hardened first exposed region.   
     
     
       14. The method of claim 11, wherein the step of treating the first exposed region comprises the steps of: heating the first exposed region; and   exposing the first exposed region to an amine vapor to form a hardened first exposed region.   
     
     
       15. A method of fabricating an integrated circuit comprising the steps of: providing a substrate wherein the substrate is transparent to ultraviolet radiation with a wavelength greater than 190 nanometers, the substrate having a front surface and a back surface;   forming an optical mask overlying the front surface of the substrate, the optical mask being opaque to ultraviolet radiation with a wavelength greater than 190 nanometers;   forming a phase shifting layer of material overlying the optical mask, the phase shifting layer being transparent to ultraviolet radiation with a wavelength greater than 190 nanometers;   depositing an image reversible photoresist layer overlying the phase shifting layer;   forming a first exposed region and an unexposed region in the image reversible photoresist layer, the first exposed region having a sidewall wherein the sidewall overlies a portion of the optical mask;   treating the first exposed region to form a hardened first exposed region;   forming a second exposed region wherein the second exposed region lies within a remaining portion of the unexposed region and is formed by exposing the back surface of the substrate to an optical illumination source;   removing the second exposed region to uncover a portion of the phase shifting layer and to form an etch mask, the etch mask comprising the hardened first exposed region and the remaining portion of the unexposed region;   etching the uncovered portion of the phase shifting layer to form a trench region; and   removing the etch mask to form a phase shifting mask;   providing a semiconductor substrate;   coating the semiconductor substrate with a photoresist layer to form a photoresist coated semiconductor substrate;   placing the phase shifting mask adjacent to the photoresist coated semiconductor substrate;   transmitting light through a portion of the phase shifting mask to define an exposure pattern in the photoresist layer; and   developing the photoresist layer to form a photoresist mask overlying the semiconductor substrate.